Atomic structure presentation

What is an Atom?
Atom comes from the Greek word atomos, which means something
invisible and cannot be cut or divided.
It was coined by Democritus in 450 BC.
But in 19th and the 20th centuries,
physicists discovered that there
are still subatomic particles
within an atom.
And therefore the name is not
appropriate anymore.

Atomic Structure
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Neutrons
Protons
Nucleus
Electrons
_
_
Atoms are made of smaller particles, called
electrons, protons, and neutrons. An atom
consists of a cloud of electrons surrounding
a small, dense nucleus of protons and
neutrons. Electrons and protons have a
property called electric charge, which
affects the way they interact with each other
and with other electrically charged particles

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Neutrons
_
_
Is a subatomic particle forming
part of the nucleus of an atom. It
has no charge. It is equal in mass
to a proton or it weighs 1 amu.
Protons
Is a positively charged
subatomic particle forming part
of the nucleus of an atom and
determining the atomic number
of an element. It weighs 1 amu.
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Electrons
_
It contribute greatly to the atom’s
charge, as each electron has a
negative charge equal to the
positive charge of a proton. It is
located in shells that surround an
atom’s nucleus.
_
Nucleus
Is the central part of an
atom, which is composed of
protons and neutrons and
contains most of an atom’s
mass.
+ +

Atomic History
Democritus
(460 BC – 37 BC)
Democritus’ Atomic
Model
Greek philosopher
the first to create an atomic model.
According to him, matter can be cut
down into smaller and smaller pieces,
until it reaches the tiniest piece called
the atom.

John Dalton
(1766 - 1844)
Born in Cumberland, England
His Theory:
 That atoms are indivisible spheres that
are neither created nor destroyed.
 Atoms of the same element are
identical.
 Atoms of different elements have
different masses.
 Atoms can be rearranged and
combined in fixed ratios to form
compoundsBowling Ball
Atomic Model

Joseph John
Thomson
(1856 – 1940)Born in Cheetham Hill, England
Discovered electron in 1897.
Used a cathode ray tube to show the atoms
of any element emit particles with a
negative charge.
Plum Pudding
Atomic Model
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_
_
_
_
_
_
_
Sea of
positive
charge
electron Discovered that the electrons
were placed randomly in a
positive matrix.
Came up with the plum pudding
model

Ernest Rutherford
(1871 – 1937)
Born in Nelson, New Zealand
Father of nuclear physics
Discovered the nucleus in 1911 when he
conducted the Gold Foil Experiment with
the help of Hans Geiger and Ernest
Marsden.
His Theory:
All the positive charges were
concentrated in the nucleus.
The negatively charged
electrons revolved around the
nucleus.
Came up with the planetary
model or nuclear model of
atom.

Niels Bohr
(1885 – 1962)
Born in Copenhagen, Denmark
His Theory:
An atom is made up of protons, which are
concentrated in the nucleus
Electrons orbit around the nucleus along
concentric orbital paths.
Electrons have quantized energy levels
and they can transfer from one orbit to
another.

James
Chadwick
(1891-1974)
English Physicist
Discovered neutron in 1932
Discovery of neutron (mass = 1.67493 x 10-24
g) explained the mass problem of many
atoms.
Nobel Prize in Physics 1935
His Theory:
 Neutrons have no electrical charge.
 Neutrons have a mass nearly equal
to the mass of a proton.
 Unit of measurement for subatomic
particles is the atomic mass unit
(amu).
electron
neutron
proton
nucleus

Isotopes Atoms of the same element having
different mass numbers and are
therefore found in the same
position in the periodic table.
 Are different versions of an
element.
 Are radioactive when they emit
radiation (radioisotopes)
Types of Radiation
• Particle radiation
- refers to alpha and beta
particles, protons, and neutrons
given off by isotopes.
• Electromagnetic radiation
- refers to gamma rays and
X-rays emitted by isotopes.

Electron Orbitals
 Is a probability function that describes where electrons may be
found.
 Are not orbits rather they are electron density clouds which
describe the highest probability distribution of electrons.
 Four types of orbitals: s, p, d, and f
s
Is a sphere, The simplest orbital and
can hold up only two electrons
p
The subshell consists of six three
dimensional lobes and can hold up to
six electrons.
d
can hold up to ten electrons. Is made
of five subshells which can hold two
electrons each.
f
made up of seven complex orbitals,
can hold fourteen electrons.

Electron Configuration
The distribution of electrons among orbitals in an atom.
An atom can be configured without drawing or illustrating any
of the s, p, d, and f orbitals.
TWO WAYS OF DETERMINING HOW ELECTRONS ARE
ARRANGED IN AN ATOM.
1. Periodic Table 2. Diagonal Rule

The Periodic Table of Elements
Elements within a group have similar
physical and chemical properties
All have the same number of
electrons in their outermost or
valence shells
Example Na
(2,8,1) and
K (2,8,8,1)
are both in
Group 1

Atomic structure presentation

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